In the field of electrophotographic toners, with the progress of electrophotographic systems, demand has arisen for development of a toner exhibiting high productivity and adaptable to high image quality and high copying speed.
As has been known, a binder resin containing crystalline polyester and amorphous polyester is used so as to meet the requirements of high image quality and high copying speed. A conventionally widely used method for producing a pulverized toner requires a step of pulverizing a melt-kneaded toner raw material containing a binder resin, wherein the pulverization time increases in proportion to reduction in size of toner particles, which may result in poor productivity. Such a problem becomes conspicuous particularly when crystalline polyester is used.
Patent Document 1 discloses a method for producing a toner, in which a binder resin containing crystalline polyester and amorphous polyester is melt-kneaded with, for example, a colorant; the kneaded product is cooled and then retained (annealed) at 45 to 65° C.; and the resultant product is subjected to a pulverization-classification step. This method is provided for the purpose of improving the productivity of a toner, in particular, pulverization performance of a toner, as well as the storage stability and low-temperature fusing property of the toner. Patent Document 2 discloses a method for producing a toner, the method including a step of melt-kneading a raw material containing crystalline polyester and amorphous polyester, a thermal treatment step, a pulverization step, and a classification step, wherein the thermal treatment step is carried out at a specific temperature for a specific period of time. This method is provided for the purpose of developing a toner exhibiting satisfactory low-temperature fusing property, pulverization performance, and storage stability. Both Patent Documents 1 and 2 relate to a method for producing a so-called pulverized toner.
As a method for producing a toner for electrostatic charge development exhibiting excellent thermal storage stability, in connection with a so-called chemically prepared toner suitable for reduction in size of toner particles, Patent Document 3 discloses a method for producing a toner, in which a resin particle dispersion prepared through phase-transfer emulsification of amorphous polyester and crystalline polyester in an aqueous medium is subjected to an aggregating-unifying step. Patent Document 4 proposes incorporation of a specific catalyst into each of amorphous polyester and crystalline polyester for the purpose of satisfying both of low-temperature fusing and stabilization of an image gloss. Patent Document 5 discloses a toner composition exhibiting improved chargeability and anti-blocking property, the toner composition containing toner particles, each particle containing a core containing at least one crystalline resin, and one or more optional ingredients selected from the group consisting of a colorant, an optional wax, and a combination thereof; and a shell containing a high-molecular-weight amorphous polyester resin having a weight average molecular weight of 10,000 to 5,000,000.